This invention relates to an exhaust gas cleaning device for an outboard motor and more particularly to an improved construction for catalytically treating the exhaust gases of an outboard motor without adversely effecting the life of the catalyst.
The problems of air pollution in connection with internal combustion engines and their exhaust products are well known. These problems exist with all applications of internal combustion engines. Two cycle engines, although they have a wide variety of applications, also present particular problems in connection with exhaust emission control due to the fact that the lubricant used to lubricate the engines is also burned in the combustion chamber and is discharged to the atmosphere along with the exhaust gases. Therefore, if any unburned lubricant remains in the exhaust gases, this can cause problems with exhaust emission. This is particularly true when the engine is utilized in conjunction with an outboard motor wherein the exhaust gases are discharged back to the atmosphere through the body of water in which the watercraft is operating. In addition to air pollution, there can also be the problem of water pollution with this type of application.
It is also known that the use of catalysts in the exhaust system can be effective in reducing unwanted exhaust gas constituents. However, even though a catalyst can be effective in treating exhaust gases, the use of catalysts present certain problems.
Specifically, the reliance on a catalyst to treat the exhaust gases can be a problem unless the catalyst has a long service life. That is, if a catalyst is employed in the exhaust system and the catalyst becomes ineffective, not only will the exhaust gas treatment become rendered ineffective or partially effective, but also the running of the engine can be deteriorated due to restriction in the exhaust gas flow.
With outboard motors, it is the normal practice to add water to the exhaust gases as they are discharged to the atmosphere, both for the purposes of cooling and silencing. In addition, the exhaust gases are normally discharged, as aforenoted, to the atmosphere through the body of water in which the watercraft is operating. It is also the normally the practice to water jacket at least a portion of the exhaust system of the outboard motor for cooling and silencing. The use of water in contact with the exhaust gases can give rise to problems in connection with catalysts. If cold water comes in contact with a catalyst bed, it can damage the bed and can also render it ineffective.
In addition to the water problems discussed in the preceding paragraph, it is normally the practice to discharge the high speed exhaust gases through an underwater discharge. Frequently, this discharge is a rearwardly facing opening formed in the hub of the propeller. When this is done, rapid decelerations or reverse operation tend to cause water to be driven backward into the exhaust system. This water can also contact the catalyst and cause the aforenoted damage.
In addition to the problems described in the preceding two paragraphs, it is also normally the practice to tilt up an outboard motor when it is not in operation. If any water is in the exhaust system, this water can come into contact with the catalyst and damage it.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a water cooled outboard motor having a catalyst treated exhaust.
It is a further object of this invention to provide a catalytic exhaust system for an outboard motor wherein water cooling is employed but wherein the water is precluded from coming into contact with a catalyst.
It is a further object of this invention to provide an improved water cooled exhaust system for an outboard motor wherein the exhaust gases are discharged to the atmosphere through the body of water in which the watercraft is operating and wherein contact of the water with the catalyst is precluded.